Optical measurement device and optical measurement method

ABSTRACT

In a first optical measurement device, light which is output from a light source is subject to linear polarizing in a polarizing unit, and is input to a test object A. Transmitted light which has passed through the test object A is orthogonally separated in an orthogonal separation unit, and the light which is orthogonally separated in the orthogonal separation. unit is received in two light receiving units. In addition, amount of light of the transmitted light is determined by a control unit, and a difference between received light levels which are received in the light receiving unit is normalized using the amount of light which is determined in a transmitted amount of light determination unit, and then the angle of optical rotation is calculated by the angle of optical rotation calculation unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.13/749,224 filed on Jan. 24, 2013. This application claims priority toJapanese Patent Application No. 2012-016737 filed on Jan. 30, 2012. Theentire disclosures of U.S. patent application Ser. No. 13/749,224 andJapanese Patent Application No. 2012-016737 are hereby incorporatedherein by reference.

BACKGROUND

1. Technical Field

The present invention relates to an optical measurement device, or thelike, for measuring an optical rotation angle.

2. Related Art

It is possible to know the composition of a material without makingdirect contact by measuring light which has passed through the material.For example, it is possible to estimate concentration of a material bymeasuring an angle of optical rotation. Optical rotation refers to aproperty in which, when linearly polarized light passes through anoptically active substance such as glucose, for example, a plane ofpolarization thereof rotates.

As a technology using the property of optical rotation, a technology isdisclosed in WO 99/30132, for example, in which linearly polarized lightwhich has passed through a test object is orthogonally separated,polarized components thereof are received by two respective lightreceiving elements, and an angle of optical rotation is measured from adifference between output levels of both the light receiving elements.

In the technology of measuring an angle of optical rotation which isdisclosed in WO 99/30132, the angle of optical rotation is measured froma difference between output levels of the two light receiving elements.However, there is a problem in this measuring method. As light which isradiated to the test object, laser light is generally used, however,there is a case in which an output fluctuation, which is referred to asa so-called return light noise, occurs in a laser device such as asemiconductor laser which outputs laser light. It is a phenomenon inwhich oscillation of a laser becomes unstable since a part of lightwhich is output from the laser device returns to the laser device againby being reflected. In this case, a so-called fluctuation in amount oflight occurs in which amount of light of transmitted light which haspassed through the test object fluctuates.

In addition, when a test object having a plurality of components whoseabsorbance is different from each other is measured, each component isnot necessarily distributed equally in the test object. That is, thefluctuation in amount of light of transmitted light which passes throughthe test object easily occurs, since the absorbance becomes differentdepending on a mixed state of each component, a radiated position of thelaser, the passage of time, or the like when performing the measuring.

When such a fluctuation in amount of light occurs, it is not possible toguarantee that the angle of optical rotation, which is simply calculatedfrom a difference between received light levels in the light receivingelements, is a correct measurement value. This is because, when thefluctuation in amount of light occurs, the received light levels in thelight receiving elements are totally changed, and the difference betweenthe received light levels is changed. For example, though it is anextreme example, when amount of light of the transmitted light isreduced to ½, a difference between received light levels is reduced to½, since the light receiving level in the light receiving element isreduced to ½. Consequently, the method of measuring an angle of opticalrotation in the related art determined from the difference in receivedlight levels, is unable to provide the correct angle of opticalrotation.

SUMMARY

An advantage of some aspects of the invention is to propose a new methodin which an angle of optical rotation can be correctly measured.

An optical measurement device according to an aspect of the inventioncomprises an orthogonal separation unit, at least two light receivingunits, and an optical rotation angle calculation unit. The orthogonalseparation unit is configured to orthogonally separate transmitted lightin which linearly polarized light has passed through a test object. Theat least two light receiving units are configured to receive light whichis orthogonally separated in the orthogonal separation unit. The opticalrotation angle calculation unit includes a transmitted light amountdetermination unit, an amplification factor setting unit, anamplification unit, and a controller. The transmitted light amountdetermination unit is configured to determine amount of light of thetransmitted light. The amplification factor setting unit is configuredto set a first amplification factor to the amount of light of thetransmitted light and set a second amplification factor to a differencebetween received light levels which are received in the light receivingunits, and the first amplification factor and the second amplificationfactor are different from each other. The amplification unit isconfigured to amplify the amount of light of the transmitted light withthe first amplification factor and the difference between the receivedlight levels with the second amplification factor. The controller isconfigured to calculate an angle of optical rotation after normalizingthe difference between the received light levels using the amount oflight of the transmitted light.

According to the optical measurement device of the aspect, the opticalrotation angle calculation unit has a subtractor obtaining thedifference between the received light levels.

According to the optical measurement device of the aspect, the opticalrotation angle calculation unit has an adder obtaining a sum of thereceived light levels which are received in the light receiving unit,and the transmitted light amount determination unit determines theamount of light using the sum of the received light levels.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a diagram which illustrates a configuration example of a firstoptical measurement device.

FIG. 2 is a table showing a data structure example of parameter data forcontrol.

FIG. 3 is a flowchart which illustrates a flow of a first angle ofoptical rotation measurement processing.

FIG. 4 is a diagram which illustrates a configuration example of asecond optical measurement device.

FIG. 5 is a flowchart which illustrates a flow of a second angle ofoptical rotation measurement processing.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, examples of preferable embodiments of the invention will bedescribed with reference to drawings. However, as a matter of course,embodiments to which the invention is applicable are not limited toembodiments described herein.

1. First Embodiment

1-1. Configuration

FIG. 1 is a diagram which illustrates a configuration example of a firstoptical measurement device 1A according to a first embodiment. The firstoptical measurement device 1A is mainly configured by including a lightsource 10, a polarizing unit 20, an orthogonal separation unit 30, alight receiving unit 40, a differential amplification unit 50, a controlunit 100, an operation unit 200, a display unit 300, a sound output unit400, a communication unit 500, and a storage unit 600.

A test object A is arranged between the polarizing unit 20 and theorthogonal separation unit 30. It is possible to set the test object Ato any sample such as a solid matter or liquid which includes anoptically active substance. In the embodiment, the test object A is setto a reagent whose main component is glucose, and a property of opticalrotation of the test object A is estimated by measuring the angle ofoptical rotation of the test object A by receiving the transmitted lightwhich passes through the test object A.

The light source 10 is a laser device which generates and outputs light.For example, the light source is configured by including a semiconductorlaser (laser diode). The light source 10 radiates laser light with aphase of a predetermined wavelength (for example, 650 nanometer [nm])from an end face which is a half mirror.

The polarizing unit 20 is a polarizing element (polarizer) whichconverts output light from the light source 10 to linearly polarizedlight, and is configured by including, for example, a polarizing opticalelement such as a polarizing prism. As the polarizing unit 20, forexample, it is possible to apply a Glan Thompson prism which is a Glantype polarizer.

In the orthogonal separation unit 30, the transmitted light in which thelinearly polarized light passed through the test object A is separatedinto orthogonal components which form a predetermined angle of aperture,that is, polarized components which are different by 90° from eachother. As the orthogonal separation unit 30, for example, it is possibleto apply the Wollaston prism as a type of polarizing optical element.

The light receiving unit 40 is an element which receives light which isorthogonally separated by the orthogonal separation unit 30, and isconfigured by including a light detector such as a photo diode. Thelight receiving unit 40 is configured by including at least two lightreceiving units. For example, the light receiving unit 40 is configuredby including a P polarized light receiving unit 40A and an S polarizedlight receiving unit 40B. In addition, the polarized components (Pcomponent and S component) which are orthogonally separated by theorthogonal separation unit 30, and are orthogonal to each other aredetected, a voltage corresponding to the amount of light is output tothe differential amplification unit 50 by performing a photoelectricconversion. In descriptions below, a voltage which is subject to thephotoelectric conversion in the P polarized light receiving unit 40A isreferred to as a “P polarization voltage”, and a voltage which issubject to the photoelectric conversion in the S polarized lightreceiving unit 40B is referred to as an “S polarization voltage”.

The differential amplification unit 50 is a calculation unit whichamplifies a difference and the sum of the received light levels in thelight receiving unit 40 for detection, and is configured by including anadder 51, a subtracter 53, a switch 55, and an amplification circuit 57.Outputs of the P polarized light receiving unit 40A and S polarizedlight receiving unit 40B are subject to an addition and subtraction inthe adder 51 and the subtracter 53, respectively, and are configuredsuch that any one of the addition result and the subtraction result isselected in the switch 55, and is amplified in the amplification circuit57. Switching of the switch 55, and the amplification factor of theamplification circuit 57 are controlled by an instruction signal fromthe control unit 100.

The control unit 100 performs switching of the switch 55 in apredetermined cycle. According to the switching control by the controlunit 100, the differential amplification unit 50 outputs a voltagecorresponding to a difference between received light levels, and avoltage corresponding to the sum of the received light levels bycalculating in a time division method. Hereinafter, descriptions will bemade by referring to the voltage corresponding to the difference betweenreceived light levels as a “subtraction output voltage”, and the voltagecorresponding to the sum of the received light levels as an “additionoutput voltage”.

In addition, the control unit 100 variably sets the amplification factorof the differential amplification unit 50 (amplification circuit 57).Specifically, when the switch 55 is switched to the subtracter 53 side,the subtraction output voltage is amplified with a first amplificationfactor “G1” by setting the amplification factor to the firstamplification factor “G1”. In contrast to this, when the switch 55 isswitched to the adder 51 side, the addition output voltage is amplifiedwith a second amplification factor “G2” by setting the amplificationfactor to the second amplification factor “G2” which is lower than thefirst amplification factor “G1”.

The control unit 100 includes a transmitted amount of lightdetermination unit 110 which determines amount of light of transmittedlight from the addition output voltage (sum of received light levels)which is output from the differential amplification unit 50, and anamplification factor setting unit 120 which variably sets anamplification factor of the differential amplification unit 50. An angleof optical rotation calculation unit 150 which calculates the angle ofoptical rotation is configured by the differential amplification unit 50and the control unit 100 in the first optical measurement device 1A.

The control unit 100 is a control unit which collectively controls eachunit of the first optical measurement device 1A, and is configured byincluding a microprocessor such as a CPU (Central Processing Unit), or aDSP (Digital Signal Processor), an ASIC (Application Specific IntegratedCircuit), or the like.

The operation unit 200 is an input unit which is configured by includinga button switch, or the like, and outputs a signal of a pressed buttonto the control unit 100. Due to an operation of the operation unit 200,various instruction inputs such as an instruction on starting themeasurement of the angle of optical rotation, and the like, areperformed.

The display unit 300 is configured by including an LCD (Liquid CrystalDisplay), or the like, and is a display unit which performs variousdisplays based on a display signal which is input from the control unit100. Information on the measured angle of optical rotation, or the likeis displayed on the display unit 300.

The sound output unit 400 is a sound output unit which outputs varioussounds based on a sound output signal which is input from the controlunit 100.

The communication unit 500 is a communication unit which transmits andreceives information which is used in the unit to and from an externalinformation processing device according to a control of the control unit100. As a communication method of the communication unit 500, variousmethods such as a type in which a wired connection is made through acable which is conformed with a predetermined communication standard, atype in which a connection is made through an intermediate device whichis used also as a battery charger which is referred to as a cradle, or atype in which a wireless connection is made using a near field wirelesscommunication are applied.

The storage unit 600 is configured by including a storage unit such as aROM (Read Only Memory), a flash ROM, or a RAM (Random Access Memory).The storage unit 600 stores a system program of the first opticalmeasurement device 1A, various programs for executing various functionssuch as a measuring function of the angle of optical rotation, data, orthe like. In addition, a work area in which data in the middle ofprocessing of various processes, a processing result, or the like istemporarily stored is included.

The storage unit 600 is stored with a first angle of optical rotationmeasurement program 610 which is read out by the control unit 100, andis executed as first angle of optical rotation measurement processing(refer to FIG. 3). The first angle of optical rotation measurementprocessing will be described in detail later using a flowchart.

In addition, the storage unit 600 is stored with parameter data forcontrol 620, output voltage data 630, and a calculated angle of opticalrotation 640.

FIG. 2 is a table showing a data structure example of a parameter datafor control 620.

The parameter data for control 620 is data which is used when thecontrol unit 100 controls the differential amplification unit 50, and isprescribed in the form of a table in which switching setting of theswitch 55, and the amplification factor of the amplification circuit 57are correlated with each other regarding the respective subtraction andaddition. The control unit 100 controls the differential amplificationunit 50 according to the parameter data for control 620.

The output voltage data 630 is data in which a voltage which is outputfrom the differential amplification unit 50 is stored. Specifically, theoutput voltage data 630 is stored with the subtraction output voltageand the addition output voltage in time sequence which are alternatelyoutput from the differential amplification unit 50 in the time divisionmethod so that it is possible to identify what output voltage it is.

In addition, the calculated angle of optical rotation 640 is data inwhich an angle of optical rotation which is calculated by the controlunit 100 is stored.

1-2. Calculation Method of Angle of Optical Rotation

A calculation method of the angle of optical rotation according to thefirst embodiment will be described in detail.

The amount of light of the transmitted light which transmitted the testobject A is set to “Ea²”, an incident angle of linearly polarized lightwith respect to the orthogonal separation unit 30 is set to “θ₀”, andthe angle of optical rotation by the test object A is set to “θ”. Atthis time, electric field components of P polarization and Spolarization are expressed by “Ea cos (θ+θ₀)”, and “Ea sin (θ+θ₀)”,respectively.

Accordingly, the P polarization voltage and the S polarization voltageare expressed by “Ea² cos² (θ+θ₀)”, and “Ea² sin² (θ+θ₀)”, respectively.

At this time, it is possible to obtain a subtraction voltage “Vs” as inthe following expression (1) by subtracting the S polarization voltagefrom the P polarization voltage. In addition, it is possible to obtainan addition voltage “Va” as in the following expression (2) by addingthe P polarization voltage to the S polarization voltage.

$\begin{matrix}\begin{matrix}{{Vs} = {{{Ea}^{2}{\cos^{2}\left( {\theta + \theta_{0}} \right)}} - {{Ea}^{2}{\sin^{2}\left( {\theta + \theta_{0}} \right)}}}} \\{= {{Ea}^{2}\left( {{\cos^{2}\left( {\theta + \theta_{0}} \right)} - {\sin^{2}\left( {\theta + \theta_{0}} \right)}} \right)}}\end{matrix} & (1) \\\begin{matrix}{{Va} = {{{Ea}^{2}{\cos^{2}\left( {\theta + \theta_{0}} \right)}} + {{Ea}^{2}{\sin^{2}\left( {\theta + \theta_{0}} \right)}}}} \\{= {{Ea}^{2}\left( {{\cos^{2}\left( {\theta + \theta_{0}} \right)} + {\sin^{2}\left( {\theta + \theta_{0}} \right)}} \right)}} \\{= {Ea}^{2}}\end{matrix} & (2)\end{matrix}$

The differential amplification unit 50 calculates the subtractionvoltage “Vs” and the addition voltage “Va” which are expressed in theexpressions (1) and (2), and amplifies the calculation result using anamplification factor which is instructed from the control unit 100.Since an amplification factor with respect to the subtraction voltage“Vs” is “G1”, and an amplification factor with respect to the additionvoltage “Va” is “G2”, the subtraction output voltage “V1” and theaddition output voltage “V2” which are output from the differentialamplification unit 50 become the following expressions (3), and (4),respectively.

$\begin{matrix}\begin{matrix}{{V\; 1} = {G\;{1 \cdot {Vs}}}} \\{{= {G\; 1}}{\cdot {{Ea}^{2}\left( {{\cos^{2}\left( {\theta + \theta_{0}} \right)} - {\sin^{2}\left( {\theta + \theta_{0}} \right)}} \right)}}}\end{matrix} & (3) \\\begin{matrix}{{V\; 2} = {G\;{2 \cdot {Va}}}} \\{= {G\;{2 \cdot {Ea}^{2}}}}\end{matrix} & (4)\end{matrix}$

It is possible to derive the following expression (5) from theexpressions (3) and (4).

$\begin{matrix}\begin{matrix}{{\frac{G\; 2}{G\; 1}\frac{V\; 1}{V\; 2}} = {{\cos^{2}\left( {\theta + \theta_{0}} \right)} - {\sin^{2}\left( {\theta + \theta_{0}} \right)}}} \\{= {\cos\; 2\left( {\theta + \theta_{0}} \right)}}\end{matrix} & (5)\end{matrix}$

Accordingly, it is possible to calculate the angle of optical rotation“θ” from the expression (5) as in the following expression (6).

$\begin{matrix}\begin{matrix}{\theta = {{\frac{1}{2}{\arccos\left( {\frac{G\; 2}{G\; 1}\frac{V\; 1}{V\; 2}} \right)}} - \theta_{0}}} \\{= {{\frac{1}{2}{\arccos\left( {C\; 1\frac{V\; 1}{V\; 2}} \right)}} - \theta_{0}}}\end{matrix} & (6)\end{matrix}$

However, it is replaced with “G2/G1=C1”.

According to the expression (6), two parameter values of “C1” and “θ₀”are necessary in order to calculate the angle of optical rotation “θ”.For example, the “C1” can be obtained from a ratio of the firstamplification factor “G1” to the second amplification factor “G2” whichis prescribed in the parameter data for control 620, and the “θ₀” can bemechanically set to a predetermined angle, or the like.

Since an angle of optical rotation which is expressed at an extremelyminute angle is set to a measurement target, the above describedparameter value greatly influences on measurement precision of the angleof optical rotation. An error which is caused by a temperature propertyof a circuit element, precision in a design value, or the like, can beincluded in the amplification factor in design (design value) of thedifferential amplification unit 50. It is also considered that themeasurement precision of the angle of optical rotation deteriorates dueto the error.

Therefore, according to the embodiment, it is possible to set the “C1”and “θ₀” by performing an initial correction. Specifically, an equationwhich derives an angle of optical rotation is set up using two or morekinds of substances whose angles of optical rotation are well-known asthe test object A. Since there are two unknown number of “C1” and “θ₀”,two unknown numbers are obtained when two or more equations are set up.A solution of the equation can be calculated using, for example, awell-known numerical calculation such as a least squares method.

1-3. Flow of Processing

FIG. 3 is a flowchart which illustrates a flow of the first angle ofoptical rotation measurement processing which is executed by the controlunit 100 according to the first angle of optical rotation measurementprogram 610 which is stored in the storage unit 600.

Firstly, the control unit 100 performs a first initial correctionprocessing (step A0). Specifically, two parameter values of “C1” and“θ₀” in the expression (6) are corrected based on the above describedmethod, or the like.

Subsequently, the control unit 100 performs an arrangement instructionof the test object A (step A1). For example, a message is displayed onthe display unit 300, or a sound guidance is output from the soundoutput unit 400. In addition, the control unit 100 causes the lightsource 10 to start radiating of laser light (step A3).

Subsequently, the control unit 100 executes a control for subtraction(step A5). Specifically, a switch switching signal S1 which switches tothe subtracter 53 side is output to the switch 55 by referring to theparameter data for control 620. In addition, a control signal forsetting the amplification factor of the amplification circuit 57 to G1is output to the amplification circuit 57. In addition, the control unit100 causes the output voltage from the differential amplification unit50 to be stored in the output voltage data 630 as the subtraction outputvoltage (step A7).

Subsequently, the control unit 100 executes a control for adding (stepA9). Specifically, a switch switching signal S2 which switches to theadder 51 side is output to the switch 55 by referring to the parameterdata for control 620. In addition, a control signal for setting theamplification factor of the amplification circuit 57 to G2 is output tothe amplification circuit 57. In addition, the control unit 100 causesthe output voltage from the differential amplification unit 50 to bestored in the output voltage data 630 as the addition output voltage(step A11).

Processes of the above described steps A5 to A11 are executed until dataof output voltages of a predetermined time is obtained (step A13). Whenthe data of output voltage of the predetermined time is obtained (Yes instep A13), the control unit 100 stops the radiation of laser light ofthe light source 10 (step A15).

Thereafter, the control unit 100 calculates the angle of opticalrotation according to the expression (6) using a parameter value whichis corrected in the first initial correction processing, a mean value ofthe subtraction output voltage, and a mean value of the addition outputvoltage of the predetermined time which is stored in the output voltagedata 630, and stores the angle of optical rotation in the storage unit600 as the calculated angle of optical rotation 640 (step A17).

In addition, it is also preferable to calculate the angle of opticalrotation “θ” using instantaneous values of the subtraction outputvoltage “V1” and the addition output voltage “V2”, however, in order toimprove calculation precision of the angle of optical rotation “θ”, itis effective when the angle of optical rotation “θ” is calculatedaccording to the expression (6) using, for example, a mean value of thesubtraction output voltage “V1”, and the addition output voltage “V2” ofthe predetermined time.

As is understood from the expression (6), according to the embodiment,the subtraction output voltage “V1” is divided by the addition outputvoltage “V2”, and the angle of optical rotation “θ” is calculated usingthe result. The addition output voltage “V2” is a voltage correspondingto amount of light of transmitted light. In addition, the subtractionoutput voltage “V1” is a voltage corresponding to a difference betweenthe received light levels. Accordingly, dividing the subtraction outputvoltage “V1” by the addition output voltage “V2” means normalizing thedifference between received light levels using the amount of light ofthe transmitted light, and the angle of optical rotation “θ” iscalculated from the difference between the normalized received lightlevels.

Returning to the descriptions in the flowchart in FIG. 3, when thecontrol unit 100 determines whether or not to end the measurement of theangle of optical rotation (step A19), and determines to continue themeasurement (No in step A19), after calculating the angle of opticalrotation, the process returns to step A1. In addition, when it isdetermined to end the measurement (Yes in step A19), the first angle ofoptical rotation measurement processing is ended.

1-4. Effects of Operation

In the first optical measurement device 1A, light which is output fromthe light source 10 becomes the linearly polarized light in thepolarizing unit 20, and is input to the test object A. The transmittedlight which transmitted the test object A is orthogonally separated inthe orthogonal separation unit 30, and the light which is orthogonallyseparated in the orthogonal separation unit 30 is received in at leasttwo light receiving units 40 (40A and 40B). In addition, the amount oflight of the transmitted light is determined in the control unit 100,the difference between the received light levels which are received inthe light receiving unit 40 is normalized using the amount of lightwhich is determined in a transmitted amount of light determination unit,and then the angle of optical rotation is calculated by the angle ofoptical rotation calculation unit 150.

If the angle of optical rotation is calculated simply using thedifference between the received light levels which are received in thelight receiving unit 40, when a fluctuation in the amount of light ofthe transmitted light occurs, it is difficult to obtain an accurateangle of optical rotation due to the fluctuation in the amount of light.However, since the amount of light of the transmitted light isdetermined, and the angle of optical rotation is calculated afternormalizing the difference between the received light levels using theamount of light in the first optical measurement device 1A, it ispossible to accurately calculate the angle of optical rotation even whenthe amount of light of the transmitted light fluctuates.

More specifically, the difference and the sum of the received lightlevels in the light receiving unit 40 are obtained in a time divisionmethod in the differential amplification unit 50. The transmitted amountof light determination unit of the control unit 100 determines theamount of light of the transmitted light using the sum of the receivedlight levels which are received in the light receiving unit 40, andnormalizes the difference between the received light levels using thedetermined amount of light of the transmitted light. With thisconfiguration, it is possible to determine the amount of light of thetransmitted light using a simple method such as obtaining the sum of thereceived light levels.

In addition, the control unit 100 variably sets the amplification factorof the differential amplification unit 50. Specifically, when thedifferential amplification unit 50 calculates the difference between thereceived light levels, the amplification factor is set to a firstamplification factor, and when the differential amplification unit 50calculates the sum of the received light levels, the amplificationfactor is set to a second amplification factor which is lower than thefirst amplification factor. Since the difference between the receivedlight levels is a minute value, it is possible to calculate the angle ofoptical rotation with high precision according to the received lightlevels by improving resolution by setting the amplification factor highcompared to a case of obtaining the sum of the received light levels.

2. Second Embodiment

2-1. Configuration

FIG. 4 is a diagram which illustrates a configuration example of asecond optical measurement device 1B in a second embodiment. The secondoptical measurement device 1B is configured by including a light source10, a polarizing unit 20, a non-polarizing separation unit 25, anorthogonal separation unit 30, a light receiving unit 40, a seconddifferential amplification unit 70, a second light receiving unit 80, anamplification unit 90, a control unit 100, an operation unit 200, adisplay unit 300, a sound output unit 400, a communication unit 500, anda storage unit 600. In addition, the same constituent elements as thosein the first optical measurement device 1A will be given the samereference numerals, and repeated descriptions will be omitted.

In the second optical measurement device 1B, the non-polarizingseparation unit 25 is provided between a test object A and theorthogonal separation unit 30. The non-polarizing separation unit 25 isa polarizing element which separates incident light into transmittedlight and reflected light in a predetermined amount of light ratio whilemaintaining a polarized state of the incident light. It is possible toapply, for example, a non-polarizing beam splitter as the non-polarizingseparation unit 25.

Light on one side which is separated by the non-polarizing separationunit 25 inputs to the orthogonal separation unit 30, and is separatedinto a P polarized component and S polarized component. In contrast tothis, light on the other side which is separated by the non-polarizingseparation unit 25 is received in the second light receiving unit 80.The light which is received in the second light receiving unit 80 issubject to photoelectric conversion, and a voltage corresponding toamount of light is output to the amplification unit 90. In addition, thelight is amplified in a predetermined amplification factor in theamplification unit 90, and then is output to the control unit 100. Thetransmitted amount of light determination unit 110 determines amount oflight of transmitted light based on received light levels of the secondlight receiving unit 80.

Since the amount of light separation proportion of the incident light bythe non-polarizing separation unit 25 is well-known, the transmittedamount of light determination unit 110 is able to calculate the wholeamount of light of the transmitted light using the light receiving levelof the second light receiving unit 80, and also to calculate the amountof light which is input to the orthogonal separation unit 30.

On the other hand, the P polarization voltage which is subject to thephotoelectric conversion in the P polarized light receiving unit 40A ofthe light receiving unit 40, and the S polarization voltage which issubject to the photoelectric conversion in the S polarized lightreceiving unit 40B are output to the second differential amplificationunit 70. In the second differential amplification unit 70, a differencebetween the P polarization voltage and the S polarization voltage iscalculated, and is output to the control unit 100 after being amplifiedwith a predetermined amplification factor. Accordingly, only thesubtraction output voltage which is mentioned in the first embodiment isoutput from the second differential amplification unit 70.

In addition, the storage unit 600 is stored with a second angle ofoptical rotation measurement program 612 which is executed as secondangle of optical rotation measurement processing (refer to FIG. 5) bythe control unit 100, output voltage data 630, and a calculated angle ofoptical rotation 640.

2-2. Calculation Method of Angle of Optical Rotation

A calculation method of the angle of optical rotation according to thesecond embodiment will be described in detail.

Transmitted light which has transmitted the test object A is subject toa non-polarizing separation into “T1:T2” by the non-polarizingseparation unit 25 (here, T1+T2=1). Specifically, amount of light “Ea²”of the transmitted light is separated into “T1:T2”, light of amount oflight “T1·Ea²” is received in the light receiving unit 40, and light ofamount of light “T2·Ea²” is received in the second light receiving unit80.

At this time, the P polarizing voltage and the S polarizing voltagewhich are received in the P polarized light receiving unit 40A and the Spolarized light receiving unit 40B, and are subject to the photoelectricconversion are expressed by “T1·Ea² cos² (θ+θ₀)” and “T1·Ea² sin²(θ+θ₀)”, respectively. Accordingly, the subtraction voltage “Vs” whenthe S polarizing voltage is subtracted from the P polarizing voltage isexpressed in the following expression (7).Vs=T1·Ea ² (cos² (θ+θ₀)−sin² (θ+θ))   (7)

On the other hand, a voltage “V” which is received in the second lightreceiving unit 80, and is subject to the photoelectric conversion isgiven in the following expression (8).V=T2·Ea ²   (8)

The second differential amplification unit 70 amplifies the subtractionvoltage “Vs” which is expressed in the expression (7) with anamplification factor “G3”. As a result, a subtraction output voltage“V3” which is output from the second differential amplification unit 70is expressed as in the following expression (9).

$\begin{matrix}\begin{matrix}{{V\; 3} = {G\;{3 \cdot {Vs}}}} \\{= {G\;{3 \cdot T}\;{1 \cdot {{Ea}^{2}\left( {{\cos^{2}\left( {\theta + \theta_{0}} \right)} - {\sin^{2}\left( {\theta + \theta_{0}} \right)}} \right)}}}}\end{matrix} & (9)\end{matrix}$

In addition, the amplification unit 90 amplifies the voltage “V” whichis expressed in the expression (8) with an amplification factor “G4”. Asa result, an output voltage “V4” which is output from the amplificationunit 90 is expressed as in the following expression (10).

$\begin{matrix}\begin{matrix}{{V\; 4} = {G\;{4 \cdot V}}} \\{= {G\;{4 \cdot T}\;{2 \cdot {Ea}^{2}}}}\end{matrix} & (10)\end{matrix}$

The following expression (11) is derived from the expressions (9) and(10).

$\begin{matrix}\begin{matrix}{{\frac{G\; 4}{G\; 3}\frac{T\; 2}{T\; 1}\frac{V\; 3}{V\; 4}} = {{\cos^{2}\left( {\theta + \theta_{0}} \right)} - {\sin^{2}\left( {\theta + \theta_{0}} \right)}}} \\{= {\cos\; 2\left( {\theta + \theta_{0}} \right)}}\end{matrix} & (11)\end{matrix}$

Accordingly, it is possible to calculate the angle of optical rotation“θ” as in the following expression (12) from the expression (11).

$\begin{matrix}\begin{matrix}{\theta = {{\frac{1}{2}{\arccos\left( {\frac{G\; 4}{G\; 3}\frac{T\; 2}{T\; 1}\frac{V\; 3}{V\; 4}} \right)}} - \theta_{0}}} \\{= {{\frac{1}{2}{\arccos\left( {C\; 2\frac{V\; 3}{V\; 4}} \right)}} - \theta_{0}}}\end{matrix} & (12)\end{matrix}$

However, it is replaced with “(G4/G3) (T2/T1)=C2”.

Similarly to the first embodiment, even in this case, it is effectivewhen determining two parameter values of “C2” and “θ₀” in the expression(12) by performing a measurement using, for example, two or moresubstances whose angles of optical rotation are known.

2-3. Flow of Processing

FIG. 5 is a flowchart which illustrates a flow of the second angle ofoptical rotation measurement processing which is executed by the controlunit 100 according to the second angle of optical rotation measurementprogram 612 which is stored in the storage unit 600. In addition, thesame steps as those in the first angle of optical rotation measurementprocessing are given the same reference numerals, and repeateddescriptions will be omitted.

First, the control unit 100 performs second initial correctionprocessing (step B0). Specifically, the two parameter values of “C2” and“θ₀” in the expression (12) are corrected based on the above describedmethod, or the like.

The control unit 100 stores the subtraction output voltage which isoutput from the second differential amplification unit 70, and theoutput voltage which is output from the amplification unit 90 in theoutput voltage data 630 of the storage unit 600 after performing a startcontrol of radiating laser light in step A3 (step B5). In addition, thecontrol unit 100 continuously stores the data of the output voltageuntil data of the output voltage of a predetermined time is obtained (Noin step A13→step B5).

When the output voltage of the predetermined time is obtained (Yes instep A13), the control unit 100 performs a stop control of radiating ofthe laser light (step A15). In addition, the control unit 100 calculatesthe angle of optical rotation according to the expression (12) using theparameter value which is corrected in the second initial correctionprocessing, and a mean value of the subtraction output voltage, and amean value of the output voltage which are stored in the output voltagedata 630, and stores the angle of optical rotation in the storage unit600 as the calculated angle of optical rotation 640 (step B17).

2-4. Effects of Operation

In the second optical measurement device 1B, transmitted light in whichthe linearly polarized light which is output from the light source 10,and is converted by the polarizing unit 20 passes through the testobject A is subject to the non-polarizing separation in a predeterminedproportion by the non-polarizing separation unit 25. In addition, lighton one side which is subject to the non-polarizing separation isreceived in the second light receiving unit 80. In addition, light onthe other side which is subject to the non-polarizing separation isorthogonally separated by the orthogonal separation unit 30. Inaddition, the control unit 100 determines the amount of light of thetransmitted light based on the light receiving level in the second lightreceiving unit 80, and calculates the angle of optical rotation afternormalizing a difference between the received light levels in the lightreceiving unit 40 using the determined amount of light.

In the second optical measurement device 1B, the difference between thereceived light levels is normalized using the amount of light which issubject to the non-polarizing separation by the non-polarizingseparation unit 25, not normalizing the difference in the received lightlevels using the amount of light of the transmitted light correspondingto the sum of the received light levels which are received in the lightreceiving unit 40. The amount of light of the transmitted light isdetermined by adopting a simple configuration in which the transmittedlight is subject to the non-polarizing separation by the non-polarizingseparation unit 25, and light on one side thereof is received in thesecond light receiving unit 80. In addition, it is possible toaccurately calculate the angle of optical rotation even when afluctuation in the amount of light of the transmitted light occurs bynormalizing the difference between the received light levels in thelight receiving unit 40 using the determined amount of light.

3. Modification Example

Embodiments to which the invention is applied are not limited to theabove described embodiments, and as a matter of course, the embodimentscan be appropriately changed without departing from the scope of theinvention. Hereinafter, modification examples will be described.

3-1. Application Example

The optical measurement devices which are described in the abovedescribed embodiments (first optical measurement device 1A, and secondoptical measurement device 1B) can be used by being incorporated inmeasuring equipment, for example, sugar measuring equipment whichmeasures sugar in fruits, blood sugar level measuring equipment whichmeasures a human blood sugar level.

When the optical measurement device is applied to the sugar measuringequipment, an angle of optical rotation is calculated by radiatinglinearly polarized light to, for example, fruit juice of fruit as a testobject A. In addition, when the optical measurement device is applied tothe blood sugar level measuring equipment, the angle of optical rotationis calculated by radiating the linearly polarized light to a portion tobe measured, by setting portions having transmitting property such as anearlobe, fingertips, epidermis parts of fingers as portions to bemeasured. In addition, the sugar of fruit, or the human blood sugarlevel can be obtained based on the calculated angle of optical rotation.

3-2. Amplification Factor of Differential Amplification Unit

In the above described embodiments, the amplification factor was set tobe switched in a case in which the difference between the received lightlevels is calculated, and in a case in which the sum of the receivedlight levels is calculated by the differential amplification unit 50 ofthe first optical measurement device 1A, however, a method of variablysetting the amplification factor of the differential amplification unit50 is not limited to this. For example, the amplification factor of thedifferential amplification unit 50 may also be variably set based on thedifference between the received light levels which are calculated in thedifferential amplification unit 50. The smaller the difference betweenthe received light levels, it is effective to set the amplificationfactor high.

In addition, when it is possible to measure absorbance of an componentwhich is included in the test object A, it is also possible to variablyset the amplification factor of the differential amplification unit 50based on the magnitude of the absorbance. When the absorbance of thecomponent which is included in the test object A is large, the amount oflight in the transmitted light is reduced. For this reason, it ispossible to perform a measurement of the transmitted light in a widedynamic range by setting the amplification factor of the differentialamplification unit 50 high, and amplifying the difference between thereceived light levels with a high amplification factor.

In addition, the amplification factor of the differential amplificationunit 50 may be variably set based on the magnitude of the angle ofoptical rotation. It is possible to measure the angle of opticalrotation in a wide dynamic range by setting the amplification factor ofthe differential amplification unit 50 high, and amplifying thedifference between the received light levels with a high amplificationfactor, when the angle of optical rotation is small.

The above described setting method of the amplification factor can besimilarly applied to the second differential amplification unit 70 ofthe second optical measurement device 1B, as well. That is, it is alsopreferable to variably set the amplification factor of the seconddifferential amplification unit 70 based on the difference between thereceived light levels which is calculated in the second differentialamplification unit 70. In addition, the amplification factor of thesecond differential amplification unit 70 may be variably set based onthe absorbance of an component which is included in the test object A,or the magnitude of the angle of optical rotation.

3-3. Calculation Method of Angle of Optical Rotation

According to the above described embodiment, the angle of opticalrotation was calculated using a mean value of an output voltage of apredetermined time, however, a calculation method of an angle of opticalrotation is not limited to this. For example, as a matter of course, theangle of optical rotation may be calculated using an instantaneous valueof an output voltage. In addition, it is also possible that angles ofoptical rotation of a predetermined time, or of a predetermined numberare calculated by repeating a step of calculating the angle of opticalrotation using the instantaneous value of an output voltage, and theangle of optical rotation is calculated by calculating the average ofthese angles of optical rotation.

3-4. Optical Element for Polarization

According to the above described embodiment, it has been described thatthe polarizing unit 20 is configured by including, for example, the GlanThompson prism, however, it is natural to have a configuration in whichother optical element for polarization than that is included. Forexample, it is also possible to have a configuration in which the GlanTailor prism which is the same Glan-type optical element forpolarization is included.

In addition, according to the above described embodiment, it has beendescribed that the orthogonal separation unit 30 is configured byincluding, for example, the Wollaston prism, however, it is possible tosuitably change the optical element for polarization which configuresthe orthogonal separation unit 30. For example, it is also possible tohave a configuration in which an optical element for polarization havinga function of orthogonal separation such as the Glan Laser prism, or alotion prism is included.

A first aspect is directed to an optical measurement device whichincludes an orthogonal separation unit which orthogonally separatestransmitted light in which linearly polarized light has passed through atest object; at least two light receiving units which receive lightwhich is orthogonally separated in the orthogonal separation unit; andan angle of optical rotation calculation unit which includes atransmitted amount of light determination unit which determines amountof light of the transmitted light, or amount of light of a predeterminedproportion of the amount of light, and calculates an angle of opticalrotation after normalizing a difference between the received lightlevels which are received in the light receiving unit using the amountof light which is determined in the transmitted amount of lightdetermination unit.

In addition, as another aspect, the embodiment may be configured as anoptical measurement method which includes orthogonally separatingtransmitted light in which linearly polarized light passes through atest object; receiving the orthogonally separated light; determiningamount of light of the transmitted light, or amount of light of thepredetermined proportion of the amount of light; and calculating anangle of optical rotation after normalizing a difference between thereceived light levels using the determined amount of light.

According to the first aspect or the like, the transmitted light inwhich the linearly polarized light passes through the test object isorthogonally separated, and the orthogonally separated light isreceived. In addition, the amount of light of the transmitted light, oramount of light of the predetermined proportion of the amount of lightis determined, and the angle of optical rotation is calculated afternormalizing the difference between the received light levels in thelight receiving unit using the determined light. By normalizing thedifference between the received light levels, it is possible tocorrectly calculate the angle of optical rotation, even in a case inwhich a fluctuation in the amount of light of the transmitted lightoccurs.

As a second aspect, the optical measurement device according to thefirst aspect may be configured such that the optical measurement deviceincludes the angle of optical rotation calculation unit which has adifferential amplification unit obtaining a difference between thereceived light levels, and further has an amplification factor settingunit which variably sets an amplification factor of the differentialamplification unit.

According to the second aspect, the difference between the receivedlight levels is obtained by the differential amplification unit. Theamplification factor of the differential amplification unit is variablyset by the amplification factor setting unit. For example, by variablysetting the amplification factor based on absorbance of the test object,and the magnitude of the angle of optical rotation, it is possible tocalculate the angle of optical rotation in a wide dynamic range.

As a third aspect, the optical measurement device according to the firstor second aspect may be configured such that the transmitted amount oflight determination unit determines the amount of light using the sum ofthe received light levels which are received in the light receivingunit.

According to the third aspect, it is possible to simply determine theamount of light of the transmitted light using the sum of the receivedlight levels which are received in the light receiving unit.

As a fourth aspect, the optical measurement device according to thefirst or second aspect may be configured such that the opticalmeasurement device further includes a non-polarizing division unit whichdivides the transmitted light using the predetermined proportion in anon-polarizing manner, and a second light receiving unit which receiveslight on one side which is divided in the non-polarizing manner arefurther included, in which the orthogonal separation unit orthogonallyseparates light on the other side which is divided in the non-polarizingmanner, and the transmitted amount of light determination unitdetermines amount of light of the transmitted light of the predeterminedrate based on the light receiving level of the second light receivingunit.

According to the fourth aspect, the transmitted light is divided at thepredetermined rate in the non-polarizing manner by the non-polarizingdivision unit. In addition, the light on one side which is divided inthe non-polarizing manner is received in the second light receivingunit. In contrast to this, the light on the other side which is dividedin the non-polarizing manner is orthogonally divided in the orthogonalseparation unit. In addition, the amount of light of the transmittedlight of the predetermined rate is determined based on the lightreceiving level of the second light receiving unit. It is possible todetermine the amount of light of the transmitted light of thepredetermined rate by adopting a simple configuration in which thetransmitted light is divided in the non-polarizing manner by thenon-polarizing division unit, and the light on one side is received inthe second light receiving unit.

The entire disclosure of Japanese Patent Application No. 2012-016737,filed on Jan. 30, 2012, is expressly incorporated by reference.

What is claimed is:
 1. An optical measurement device comprising: anorthogonal separation unit configured to orthogonally separatetransmitted light in which linearly polarized light has passed through atest object; at least two light receiving units configured to receivelight which is orthogonally separated in the orthogonal separation unit;and an optical rotation angle calculation unit including a transmittedlight amount determination unit configured to determine amount of lightof the transmitted light, an amplification factor setting unitconfigured to set a first amplification factor to the amount of light ofthe transmitted light and set a second amplification factor to adifference between received light levels which are received in the lightreceiving units, the first amplification factor and the secondamplification factor being different from each other, an amplificationunit configured to amplify the amount of light of the transmitted lightwith the first amplification factor and the difference between thereceived light levels with the second amplification factor, and acontroller configured to calculate an angle of optical rotation afternormalizing the difference between the received light levels using theamount of light of the transmitted light.
 2. The optical measurementdevice according to claim 1, wherein the optical rotation anglecalculation unit has a subtractor obtaining the difference between thereceived light levels.
 3. The optical measurement device according toclaim 1, wherein the optical rotation angle calculation unit has anadder obtaining a sum of the received light levels which are received inthe light receiving unit, and the transmitted light amount determinationunit determines the amount of light using the sum of the received lightlevels.